Cossack population before the bolshevist revolution

By the end of the 19th century the number of Cossack groups had expanded to 11,
including the Don, Kuban, Terek, Astrakhan, Ural, Orenburg,
Semirechen, Siberian, Transbaikal (Zabaikal'skie kazaki), Amur
and Ussuri (click to see the map of Cossack Hosts). In tsarist
Russia the Cossacks usually lived in special settlements near the country's borders. Every
Cossack man was liable for military service to the Tsar, having to provide his own horse,
uniform, saber, lance, saddle, etc. Cossacks fulfilled border guard and territorial
militia functions, being in a sense "a live fence" of Russia. In exchange,
Cossacks had a number of economic privileges. For four centuries until the 1917 Bolshevik
revolution, Russia relied on free Cossack warriors to defend and expand its southern and
eastern frontiers.

Cossacks were always free, even during the centuries when Russia, Prussia, Poland and
other states in the region had serfdom law. Cossacks had freedom, special economical
privileges and lands to own - in exchange for their military service to the Tsars. It were
the Cossacks that extended Russia's territories into Caucasus,
Central Asia, Siberia, Russian Far East and even North America (Alaska and Northern
California).

When WWI was announced, there were 104 Cossack regiments and 161 separate sotnya
mobilized. Cossacks were widely used both on the Western front (against Germany and
Austro-Hungary) and in the South (Turkey).